Continuous casting mold and processes for making and retrofitting

ABSTRACT

An important liner for use in a continuous casting machine includes the conventional hot face surface, cold face surface, and at least one coolant interface area, such as the bottom of a cooling clot that is machined into the liner. Advantageously, the coolant interface area is configured to have a shape along at least a portion of its length that differs from the simple planar shape that is usual for such areas. This shape could include a fin that projects from the coolant interface surface, a corrugation, or other shape. As a result of this configuration, the surface area of the coolant interface area is maximized, thereby promoting enhanced heat transfer through the liner at a portion of the liner that is proximate the coolant interface area. This configuration can be placed selectively at certain areas of the mold that are felt to need increased thermal conductivity, such as near the meniscus area, and in areas where premature mold wear or cracking have been observed due to thermal stresses. A process for making and retrofitting a mold is also described.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates broadly to the field of metal production and casting. More specifically, this invention relates to an improved mold; process for making a mold; and process for retrofitting a mold for a continuous casting system that results in longer useful mold life, improves the uniformity of heat removal, and, most importantly, turns out a better product than conventional continuous casting molds do.

[0003] 2. Description of the Related Technology

[0004] A conventional continuous casting mold includes a number of liner plates, usually made of copper, and outer walls surrounding the liner plates. A conventional such liner plate or “mold insert” 10 is depicted in FIG. 1. One side 16 of a liner plate 10 defines a portion of the mold, commonly termed the “hot face,” 12 that contacts the molten metal during the casting process. The other side of the liner plate 10 is commonly termed the “cold face” 14. Coolant interface areas 18, which are usually embodied as parallel vertically extending water circulation slots 19 or passageways are provided between the outer wall and the cold face 14 of the liner plate 10 to cool the liner plate 10 so as to induce a heat flux away from the nascent casting, through the liner and out of the casting machine via the water coolant. Slots 19 have a bottom surface 20 that is generally planar. During operation, water is introduced to these slots 19, usually at the bottom end of the mold, from a water supply via an inlet plenum that is in communication with all of the slots in a liner plate. The cooling effect so achieved causes an outer skin of the molten metal to solidify as it passes through the mold. The solidification is then completed after the semi-solidified casting leaves the mold by spraying additional coolant, typically water, directly onto the casting. This method of metal production is highly efficient, and is in wide use in the United States and throughout the world.

[0005] In most continuous casting machines the molten metal is introduced into the mold from a tundish through a refractory nozzle that is submerged within the mold. As a result of the constant introduction of molten metal through the nozzle ports, the shape of the mold, and the cooling effect that is applied by the hot face of the mold, hot metal or molten metal circulation currents form within the mold and, through the well documented heat transfer medium of convection, cause the cooling rate to be uneven over the surface of the hot face. This can cause uneven deterioration of the hot face, and contribute to premature mold failure. It can also impact adversely on the quality of the cast product. One example of this may be found in the operation of funnel-type molds. A funnel-type mold is used to cast a thin slab product, and includes, at the introduction end of the mold, a relatively wide central region, relatively narrow end regions, and transition regions between the central region and the end regions. The refractory nozzle is inserted into the central region, and, it has been found in practice, premature wear and failure of the mold tend to occur at the transition regions. Funnel molds operate at higher temperatures and at higher casting speeds than conventional molds. As a result, the cooling slots in these types of mold tend to experience a phenomenon known as nucleate boiling, which generally results in scale deposits that act as a thermal insulator between the cooling water and the material of the liner. This in turn causes a reduction in heat transfer that results in even hotter surface temperatures on the hot face which, can cause accelerated cracking and crack propagation..

[0006] Another example of the effect described above may be found in specialized molds that are used to cast structural members such as I-beams. These molds are wider at the ends and narrow at the center, and, as in funnel-type molds, premature cracking and wear tends to occur at the transition areas.

[0007] In addition to problems that tend to plague the specialized molds described above, individual molds of any configuration may experience recurring problems due to uneven heat flux through the mold liner.

[0008] For the reasons described above, a need exists for an improved continuous casting mold that is as resistant as possible to degradation of the hot face as a result of uneven heat flux. In addition, a need exists for a process for making such a mold, and for a process for retrofitting existing molds in order to make them as resistant as possible to degradation of the hot face as a result of uneven heat flux.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the invention to provide an improved continuous casting mold that is as resistant as possible to degradation of the hot face as a result of uneven heat flux.

[0010] It is further an object of the invention to provide a process for making such a mold, and a process for retrofitting existing molds in order to make them as resistant as possible to degradation of the hot face as a result of uneven heat flux.

[0011] In order to achieve the above and other objects of the invention, a liner for use in a continuous casting machine includes a hot face surface; a cold face surface that includes at least one coolant interface area that is adapted to contact a coolant for transferring heat away from the liner during operation; and wherein the coolant interface area is configured to have a shape along at least a portion of its length that differs from a simple planar shape that is usual for such coolant interface areas, whereby surface area for said coolant interface area is maximized, thereby promoting enhanced heat transfer through the liner at a portion of the liner that is proximate the coolant interface area.

[0012] According to a second aspect of the invention, a process of retrofitting a liner for a continuous casting mold in order to optimize heat transfer characteristics of the liner during operation includes steps of (a) removing a liner from a continuous casting mold; (b) modifying a shape of at least a portion of a coolant interface area on a cold face of the mold in order to change a surface area of said portion; and (c) placing the liner into service in a continuous casting mold, whereby enhanced heat transfer through the liner is promoted at areas that are proximate to the portion of the coolant interface area.

[0013] According to a third aspect of the invention, a liner for use in a continuous casting machine includes a hot face surface; and a cold face surface that includes at least one coolant interface area that is adapted to contact a coolant for transferring heat away from the liner during operation. The coolant interface area is configured to have a shape along at least a portion of its length that differs from a simple gun-drilled shape, so that surface area for the coolant interface area is maximized, thereby promoting enhanced heat transfer through the liner at a portion of the liner that is proximate said coolant interface area.

[0014] These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a diagrammatical perspective view of a conventional mold liner;

[0016]FIG. 2 is a diagrammatical perspective view of a mold liner that is constructed according to a first embodiment of the invention;

[0017]FIG. 3 is a cross-sectional view taken through a mold liner that is constructed according to a second embodiment of the invention;

[0018]FIG. 4 is another, different cross-sectional view taken through the mold insert that is shown in FIG. 3;

[0019]FIG. 5 is a diagrammitical depiction of a portion of the mold insert that is shown in FIGS. 3 and 4;

[0020]FIG. 6 is a diagrammitical depiction of one step in a process that is performed according to a preferred embodiment of the invention;

[0021]FIG. 7 is a cross-sectional depiction of a funnel-type mold that is configured according to one embodiment of the invention;

[0022]FIG. 8 is a cross-sectional view showing a beam blank mold that is constructed according to another: preferred embodiment of the invention; and

[0023]FIG. 9 is a diagrammatical view depicting a radiused corrugation according to an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0024] Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIG. 2, a mold liner 22 for use in a continuous casting machine includes a hot face surface 24 and a cold face surface 28 that includes at least one coolant interface area 30, which is embodied as a slot 31, for transferring heat away from the mold liner 22 during operation by providing a path through which a coolant can flow. As may be seen in FIG. 2, the coolant interface area 30 is configured to have a shape along at least a portion of its length that differs from the simple planar surface 20 shown in the conventional liner construction that is depicted in FIG. 1. In the embodiment of the invention that is shown in FIG. 2, coolant interface area 30 is configured to include a fin element 32 for increasing the surface area of the interface area 30 in order to promote enhanced heat transfer at the portion of the liner 22 that is nearby the coolant interface area 30. Preferably, this increase in surface area is effected with a minimum of increase in the average volume or mass that separates the slot surface from the hot face surface of the mold. The goal is to maximize the ratio of convective heat transfer at the slot bottom to the conductive heat resistance of the material that is positioned between the cooling slot and the hot face surface. To maximize the former, surface area should be maximized. To minimize the latter, mass and volume should be minimized. The optimal configuration for effecting this goal is felt to be a fin. However, certain alternative configurations, such as corrugations, might also have beneficial effect and might be less difficult to machine into the slot bottom surface. According to the invention, fins or corrugations could also be placed on one or more side surfaces of the cooling slots.

[0025] Referring now to FIG. 3, it will be seen that a mold liner 23 that is constructed according to a second, alternative embodiment of the invention will be shown and described. In this embodiment, the coolant interface area is configured to have a shape that differs from a simple planar shape along a portion of its length that is proximate to a meniscus region 26 of the hot face surface. More specifically, mold liner 23 includes three fins 42, as may also be seen in cross section in FIG. 4. Each of the fins is tapered at one end 34 so as to minimize potential for cavitation damage to the coolant interface area. In addition, the fins are shaped and oriented so as to have an axis that is substantially parallel to an intended direction of coolant flow over the fin 42. As may be seen in FIG. 3, the slot 31 is connected at its top end to a plenum 38. The lower end is similarly constructed, so that coolant such as water can continuously be circulated through the slot 31 for purposes of cooling the mold.

[0026] Looking now to FIG. 4, mold insert 23 is configured so at to have a slot width d₁ a distance d₂ that is defined as from one side of the slot to the center most part of the furthermost fin 42, a distance d₃ that is defined as the distance from the side of the slot to the center line of the centermost fin 42 and a distance d₄ that is defined as that from the side of the slot to the center of the most near fin 42. The slots are separated in this embodiment by a distance d₅ and, as is better shown in FIG. 5, the fins are preferably of a outermost width d₆ at their bases, and of a minimum width d₇ at or near their distal ends. The fins 42 further project a distance d₈ from the bottom of the slot 31 and are separated from each other centerline by a distance d₉.

[0027] In either embodiment of the invention, the fins 42 can be formed unitarily with the slot bottom, such as by machining the slot bottom to form the fins, or can be applied to the slot bottom through a joining process such as brazing or welding. FIG. 6 diagrammatically depicts a fin element 46 being joined to a planar surface 20 of a conventional mold insert as part of a process for retrofitting the insert which will be discussed in greater detail below.

[0028] Referring now to FIG. 7, it has been found that the present invention has particular utility for mold liners 48 of the type that are used in funnel-type conventional casting molds. As described above, these types of molds are particularly sensitive to degradation in the transition regions 54 that are positioned between the wide central areas 50 of the mold and the narrow end regions 52. As may be seen in FIG. 7, to combat this problem it is proposed to provide cooling enhanced slots 60 that are enhanced according to the principles of the invention at the transition regions 54. Non-enhanced slots 56, 58 may continue to be used at the end regions 52 and the central region 50, respectively. Alternatively, cooling enhanced slots could be provided throughout the entire mold, or, by varying the number and shapes of the fins in the slots, cooling may be enhanced throughout the mold, but more in certain selected areas such as by the transition regions 54. For example, a fin may be placed in the slot area at an upper portion of the mold, where enhanced cooling is desirable, but the slot may be left unmodified at a lower part of the mold, where enhanced cooling is not needed or desired.

[0029] Similarly, as shown in FIG. 8, a liner for a beam blank mold 62 includes a pair of wide end areas 66, a narrow central area 64 and a transition region 68 that tends to be susceptible to premature cracking and failure, particularly at the meniscus region, and particularly near the interface of the transition region and the narrow central area 64. As may be seen in FIG. 8, the slots 72 that are positioned near the transition region 66 are cooling enhanced according to the principles of the invention, while the slots 70, 74 at the end area 66 and the central area 64, respectively, are not so enhanced. As in the funnel-type mold described above, alternatively enhanced cooling could be provided in all of the slots, or by varying degree in one or more of the slots. Frequently, the cooling slots in a beam blank mold are gun-drilled, rather than rectangular in cross section. In this case, it is possible to incorporate the invention by machining corrugations, fins, or other irregularities that increase the surface area, by a process such as EDM machining or supplemental gun-drilling, into the surface of the gun-drilled hole, preferably in the side of the gun-drilled hole that is closest to the hot face.

[0030]FIG. 9 depicts an embodiment wherein the fins are machined into the slot bottom as a radiused corrugation. Although these fins might not be as efficient as rectangular fins, they may in some cases be easier to make or to retrofit into an existing mold.

[0031] A continuous casting mold may be originally manufactured according to the principles of the invention, but the invention has particular utility for retrofitting existing molds, based on known patterns of Wear and premature failure of a type of mold or of a specific mold. In operation, a process of retrofitting a mold liner for a continuous casting mold in order to optimize heat transfer characteristics of the liner during operation will include steps of removing a liner from a continuous casting mold, modifying a shape of at least a portion of a coolant interface area on a coldface of the mold in order to change a surface area of the portion; and placing the liner into service in :a continuous casting mold. To modify the shape of the coolant interface area, fins can be machined in the slot bottom, or, as is diagrammatically shown in FIG. 6, a fin element 46 may be secured to the slot bottom 20 by a method such as welding or brazing.

[0032] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A liner for use in a continuous casting machine, comprising: a hot face surface; a cold face surface, said cold face surface comprising at least one coolant interface area that is adapted to contact a coolant for transferring heat away from said liner during operation; and wherein said coolant interface area is configured to have a shape along at least a portion of its length that differs from a simple planar shape that is usual for such coolant interface areas, whereby surface area for said coolant interface area is maximized, thereby promoting enhanced heat transfer through the liner at a portion of said liner that is proximate said coolant interface area.
 2. A liner according to claim 1 , wherein said cold face surface has a plurality of coolant interface areas, and less than all of said coolant interface areas are configured to have a shape that differs from a simple planar shape, whereby heat transfer is promoted only in certain predetermined areas of said liner.
 3. A liner according to claim 2 , wherein said liner is configured for a funnel-type continuous casting mold, and at least one coolant interface area that is proximate a transition region between a wide central region and a narrow end region is configured to have a shape that differs from a simple planar shape.
 4. A liner according to claim 2 , wherein said liner is configured for a beam blank type continuous casting mold, and at least one coolant interface area that is proximate a transition region between a wide end region and a narrow central region is configured to have a shape that differs from a simple planar shape.
 5. A liner according to claim 1 , wherein said coolant interface area is configured to have a shape that differs from a simple planar shape along a portion of its length that is proximate to a meniscus region of said hot face surface.
 6. A liner according to claim 1 , wherein said shape that differs from a simple planar shape comprises at least one fin projecting from coolant interface area.
 7. A liner according to claim 6 , wherein said fin is unitary with said liner.
 8. A liner according to claim 6 , wherein said fin is joined to said liner.
 9. A liner according to claim 6 , wherein said fin is shaped so as to have an axis that is substantially parallel to an intended direction of coolant flow over said fin.
 10. A liner according to claim 6 , wherein said fin is shaped so as to have a tapered trailing edge with respect to an intended direction of coolant flow over said fin so as to minimize potential for cavitation damage to said coolant interface area.
 11. A liner according to claim 1 , wherein said shape that differs from a simple planar shape comprises a corrugated shape.
 12. A process of retrofitting a liner for a continuous casting mold in order to optimize heat transfer characteristics of the liner during operation, comprising steps of: (a) removing a liner from a continuous casting mold; (b) modifying a shape of at least a portion of a coolant interface area on a cold face of said mold in order to change a surface area of said portion; and (c) placing the liner into service in a continuous casting mold, whereby enhanced heat transfer through the: liner is promoted at areas that are proximate to said portion of said coolant interface area.
 13. A process according to claim 12 , wherein step (b) is performed on less than all of the coolant interface areas on the liner.
 14. A process according to claim 12 , wherein said liner is configured for a funnel-type continuous casting mold, and step (b) comprises modifying at least one coolant interface area that is proximate a transition region between a wide central region and a narrow end region to have a shape that differs from a simple planar shape.
 15. A process according to claim 12 , wherein said liner is configured for a beam blank type continuous casting mold, and step (b) comprises modifying at least one coolant interface area that is proximate a transition region between a wide end region and a narrow central region to have a shape that differs from a simple planar shape.
 16. A process according to claim 12 , wherein step (b) comprises modifying the coolant interface area to have a shape that differs from a simple planar shape along a portion of its length that is proximate to a meniscus region of said hot face surface.
 17. A process according to claim 12 , wherein step (b) comprises providing at least one fin that projects from coolant interface area.
 18. A process according to claim 17 , wherein step (b) comprises providing at least one fin that projects from coolant interface area so as to be unitary with said liner.
 19. A process according to claim 17 , wherein step (b) comprises providing at least one fin that projects from coolant interface area so as to be joined to said liner.
 20. A process according to claim 18 , wherein step (b) is performed so that said fin is shaped so as to have an axis that is substantially parallel to an intended direction of coolant flow over said fin.
 21. A process according to claim 18 , wherein step (b) is performed so that said fin is shaped so as to have a tapered trailing edge with respect to an intended direction of coolant flow over said fin so as to minimize potential for cavitation damage to said coolant interface area.
 22. A process according to claim 12 , wherein step (b) is performed so that said shape that differs from a simple planar shape comprises a corrugated shape.
 23. A process according to claim 17 , wherein step (b) comprises joining a fin to said coolant interface area by a method that is selected from the group including brazing and welding.
 24. A liner for use in a continuous casting machine, comprising: a hot face surface; a cold face surface, said cold face surface comprising at least one coolant interface area that is adapted to contact a coolant for transferring heat away from said liner during operation; and wherein said coolant interface area is configured to have a shape along at least a portion of its length that differs from a simple gun-drilled shape that is usual for such coolant interface areas, whereby surface area for said coolant interface area is maximized, thereby promoting enhanced heat transfer through the liner at a portion of said liner that is proximate said coolant interface area. 